1. Field of the Invention
This invention relates to a magnetic recording medium and methods of post treatment of the magnetic layer of such media after initial media fabrication to improve their perpendicular magnetization for high density recording of signals.
2. Description of the Prior Art
In the technology of conventional magnetic recording using tape, sheet or disk recorders in video, audio or other digitized information storage, the signals are recorded on a magnetic recording layer formed on a non-magnetic base by magnetizing the layer in the plane of the film in a longitudinal direction, which direction is parallel to the direction of relative movement of the medium to the recording transducer or head. This has been referred to as the longitudinal magnetization mode. In a recording process, the information (or bits) to be stored is recorded by changing the state or direction of the magnetization, i.e., a bit of information is created by reversing the magnetization direction of the magnetic medium or creating a flux reversal. When recording in the longitudinal magnetization mode, a strong demagnetization field is created between oppositely magnetized areas on the medium. The existence of this demagnetization field in the longitudinal magnetization recording mode causes attenuation and rotation of the residual magnetization, with the result that an attenuated output is obtained in reproducion of the recorded signal. This attenuation and signal deterioration is accentuated as the linear packing density is increased or the wavelength of recorded signals is decreased in the direction of longitudinal magnetization. The consequence is a limitation on the maximum recording density capable in the longitudinal magnetization mode.
If the magnetic layer can support principally a magnetization normal to the film plane at the remnants, then, if signals are recorded by reversing the magnetization direction in the direction normal to the surface of the magnetic layer following the pattern of the signal (i.e., recording in the so-called perpendicular magnetization mode), decreasing the wavelength of the recorded signal, as by increasing the recording density, causes a reduction in the demagnetizing field. Therefore, it will be appreciated that, for an increase in the density of information to be stored in a given area of the magnetic recording medium, recording in the perpendicular magnetization mode (hereinafter referred to as perpendicular recording) is more advantageous than the conventional recording using longitudinal magnetization mode (hereinafter referred to as longitudinal recording).
In order to overcome the problems associated with the existing proposed methods of producing a magnetic recording medium for perpendicular recording, an alternative method to produce such magnetic recording media having a highly oriented easy axis of magnetization perpendicular to film plane for perpendicular recording medium and which can be fabricated at an extremely low cost, rendering it highly adaptive to and competitive for a multitude of perpendicular recording applications. Although this method is explained in detail herein, the subject matter thereof is the basis of patent application Ser. No. 306,127 filed Sept. 28, 1981 and filed concurrently herewith. This invention relates to post treatment of such media to enhance the perpendicular magnetization hysteretic properties. Other post treatment techniques are the subject matter and basis of patent application Ser. No. 306,126 filed Sept. 28, 1981, and filed concurrently herewith.